An abrupt change in source materials for Chinese loess deposits at the Pliocene-Pleistocene boundary: Insights from K isotopes and modeling

Abstract

The eolian deposits on the Chinese Loess Plateau (CLP) are key archives of late Cenozoic climate changes and atmospheric circulation, However, the long-standing controversy about the stability of dust sources over the last ∼ 6 Myr limits our understanding of the genesis of the CLP and its paleoenvironment implications. Here we report that an abrupt decrease in K isotope compositions (δ⁴¹K) of the CLP eolian deposits occurred at ∼2.58 Ma, with loess/paleosol displaying δ⁴¹K values (-0.41 ‰ to -0.63 ‰) lower than the bulk-silicate-earth-like Red Clay values (-0.35 ‰ to -0.45 ‰). Furthermore, The δ⁴¹K values of eolian deposits are negatively correlated with the Na₂O/K₂O and Na₂O/Al₂O₃ ratios, with negligible influence from different grain size fraction. These observations indicate that the δ⁴¹K values are not controlled by post-depositional weathering at the CLP, but rather by an increased export of weathered detritus or recycled sediments from the Northeastern Tibetan Plateau, as revealed by K isotope surveys of potential source materials and Earth system model simulations. Our results further suggest that the intensified global cooling during the Quaternary promoted greater sediments erosion and altered the dynamics of the westerlies and the Siberian High, with important implications for understanding the paleoenvironment changes and reconstruction of the East Asian atmospheric circulation across the Pliocene-Pleistocene boundary.